Is it okay to fast for a long time?

Fasting for a few days probably won't affect most healthy people, as long as dehydration is not present. But long-term complete fasting or intermittent fasting can be detrimental to your health.
Because, the body needs vitamins, minerals and other nutrients from food to maintain and grow. If you don't get enough, you can experience symptoms such as: Fatigue, dizziness, constipation, dehydration and inability to tolerate cold temperatures. Here you can also answer the question of fasting for a long time? Fasting for too long or too often can be life-threatening.

2.1. Short-Term Fasting 5:2 Model: Limit your calorie intake to two days per week (500 calories per day for women and 600 for men). 6:1 Model: This model is similar to 5:2, but with only one day of reduced calorie intake instead of two. 16:8 Model: This model involves consuming food only over an 8-hour period and fasting for 16 hours a day, every day of the week. Most of these models recommend short quick times of 8–24 hours. However, some people choose to fast for much longer 48 and even up to 72 hours.

Longer periods of fasting increase the risk of fasting-related problems. This includes dehydration, irritability, mood swings, fainting, hunger, lack of energy, and inability to concentrate.
The best way to avoid these side effects is to stick to a shorter fasting period, up to 24 hours - especially when you're just starting out. If you want to increase your fasting time to more than 72 hours, you should contact your doctor for assistance.
2.2 Eat fast but eat small portions Fasting involves eliminating some or all of food and drink over a period of time. While you can eliminate food completely on fasting days, some fasting patterns like the 5:2 diet allow you to consume about 25% of your calories in a day.
If you want to try fasting, you can apply calorie restriction so that you still eat a small amount on your fasting days - a safer option than fasting entirely. This approach can help reduce some of the risks associated with fasting, such as feeling weak, hungry, and unfocused. It can also make fasting more sustainable since you probably won't feel hungry.
2.3. Stay hydrated: Mild dehydration can lead to fatigue, dry mouth, thirst, and headaches – so it's important to stay hydrated while fasting. Most health authorities recommend the 8×8 rule – totaling just under 2 liters of fluid per day – to stay hydrated.
However, the actual amount of liquid you need is quite individual. Since you get about 20-30% of the fluids your body needs from food, it's fairly easy to become dehydrated while fasting.
During fasting, many people aim to drink 8.5–13 cups (2–3 liters) of water throughout the day. However, your thirst will tell you when you need to drink more, so listen to your body.
2.4. Don't disrupt the big parties After a period of limited eating, you can celebrate by eating a hearty meal. However, breaking the fast with a party can leave you feeling bloated and tired. Also, if you want to lose weight, partying can harm your long-term goals by slowing or halting your weight loss. Because total calories affect weight, consuming too many calories after fasting will reduce your calorie deficit. The best way to overcome hunger is to continue eating normally and return to your normal eating habits.

2.5. Stop fasting if you feel unwell During the fast you may feel a little tired, hungry and irritable - but sometimes you may not feel well. To keep yourself safe, especially if you're new to fasting, consider limiting your fast to 24 hours or less and have a snack ready in case you start to feel sick. You may feel faint or sick.
If you are sick or worried about your health, stop fasting immediately.
Some signs that you should stop fasting and seek medical help include: fatigue or weakness that prevents you from performing daily tasks, as well as feeling sick and uncomfortable doubt.
2.6. Eat enough protein Many people start fasting as a way to try to lose weight. However, a calorie deficit can cause your body to lose muscle along with fat. To minimize muscle loss while fasting, you need to make sure you eat enough protein.
Also, if you eat small amounts on fasting days, including some protein may provide other benefits, including controlling your hunger.
Some studies show that consuming about 30% of a meal's calories from protein can significantly reduce appetite. Therefore, eating some protein on fasting days can help offset some of the side effects of fasting.
2.7. Eat more whole foods on non-fasting days Most people who fast are trying to improve their health. While fasting involves fasting, it's still important to maintain a healthy lifestyle on the days you're not fasting.
A healthy diet based on whole foods has been linked to many health benefits, including a reduced risk of cancer, heart disease, and other chronic diseases.
You can make sure your diet stays healthy by choosing whole foods like: meat, fish, eggs, vegetables, fruits and legumes when you eat them.

2.8. Maintain gentle exercise Some people find that they can maintain a regular exercise regimen while fasting. However, if you are new to fasting, it is best to maintain all exercises at a low intensity. Low-intensity exercises can include walking, light yoga, gentle stretching, and housework. Most importantly, listen to your body and rest if you're having trouble exercising while fasting.
Although short-term fasting is generally considered safe, the following people should not attempt to fast without consulting a medical professional:
People with medical conditions such as heart disease or type 2 diabetes Women who are trying to conceive, get pregnant or breastfeed People who are underweight People who have had an eating disorder People with low blood pressure People who are taking prescription medications Women with a history of amenorrhea Older people Teenagers To stay healthy while fasting, it's best to do short fasts, avoid intense exercise, and stay hydrated. Eating enough protein and keeping a balanced diet when you're not fasting can also maintain overall health and ensure successful fasting.
Hope the above information has provided you with more options and answers if it's okay to fast for a long time. Wish you always have a scientific diet and improve your work productivity and improve your life.

References: healthline.com, webmd.com